1. Field of the Invention
The present invention relates to interworking between a mobile communication network and a wireless local area network (WLAN). More particularly, the present invention relates to an apparatus and a method for transmitting WLAN information in a mobile communication network.
2. Description of the Related Art
Recently, as portable electronic appliances including portable computers and mobile phones have been rapidly developed, many studies and research have been performed in relation to wireless access schemes for a wired network, such as an Intranet, the Internet or the World Wide Web (WWW). A wireless local area network (WLAN) is known as a technology to access the wired network at a high rate with a low cost. In addition, 3rd generation mobile communication systems, such as the code division multiple access (CDMA) 2000, the wideband code division multiple access/universal mobile telecommunications system (WCDMA/UMTS), the general packet radio system (GPRS) or the evolution data and voice (1×EV-DV), may attain high rate data transmission through wireless channels so that the mobile station or user equipment can access the packet communication network, such as the Internet, through a cellular mobile communication network.
However, such advancements may cost a lot in wireless access technologies. For this reason, studies and research are currently focused on interworking terminals capable of accessing both the mobile communication network and the WLAN in order to attain interworking between the mobile communication network and the WLAN. The main purpose of the interworking is to provide services of the mobile communication network by using the WLAN, which is a mass storage network constructed at a low cost.
Differently from the mobile communication network, the IEEE 802.11 WLAN does not use a paging channel for tracking accessible network nodes, that is, access points. An operation of an IEEE 802.11 interworking terminal for detecting the access points is called a “scan”. The scan scheme of the WLAN may be divided into an active scan and a passive scan. According to the active scan, the terminal transmits a probe signal in order to probe access points in the vicinity of the terminal. Upon receiving the probe signal, the access point sends a response signal comprising various parameters required for accessing the access point, so that the terminal can recognize the access points. Although the terminal can rapidly find the access points by using the active scan, power consumption of the terminal may increase. According to the passive scan, the access points may transmit a beacon signal to a peripheral area thereof every several hundred milliseconds and the terminal receives the beacon signal, thereby recognizing the access points. Since the beacon signal comprises various parameters required for the terminal to access the WLAN, the terminal receiving the beacon signal can access the corresponding access point. Although the terminal employing the passive scan can reduce power consumption as compared with the terminal employing the active scan, the terminal cannot find the access points as rapidly.
In the case of a WLAN according to the IEEE 802.11 standard, it is difficult for the terminal to find the WLAN allowing access to the terminal, and in particular, a WLAN capable of interworking with the mobile communication network. That is, in order to scan all access points when the access points of the WLAN operate in mutually different frequency bands, the terminal must transmit probe signals through various frequency channels (active scan) or the terminal must search various frequency channels to receive the beacon signals of the frequency channels (passive scan). Thus, the time for finding a WLAN may increase. If the terminal continuously performs the scan operation to find a WLAN, power consumption of the terminal may significantly increase.
Therefore, the WLAN can provide an indicator for directing cells to perform the WLAN scanning by using system information broadcasted from the mobile communication network or can provide detailed WLAN information, for example, frequency information, a WLAN identifier: service set identifier (SSID) and the like for the purpose of fast WLAN scan.
FIG. 1 is a schematic view illustrating WLAN-interworking (WLAN-I) in a conventional mobile communication system.
Referring to FIG. 1, WLAN information 115 is transmitted by using system information broadcasted from a node B 100 provided in a cell 110 comprising a WLAN area 120. Terminals 101 through 107 are WLAN-I terminals. The node B 100 provides the terminals 101 to 107 with the WLAN information 115 indicating that the WLAN area exists in the cell so that the terminals 101 to 107 scan the WLAN and then are handed over to the WLAN area 120.
The WLAN area 120 is significantly smaller than the cell 110 of the mobile communication network. Thus, if the terminals 101 to 105 and 107 except for the terminal 106 adjacent to the WLAN area 120 perform the WLAN scanning, power consumption may unnecessarily increase. This problem may become severe as the size of the WLAN area 120 is reduced relative to the size of the cell 110. In addition, although the WLAN area 120 is concentrated on a hot spot area in the cell, terminals located in other areas also perform the WLAN scan so that power consumption of the terminals may increase. In view of a network, the conventional mobile communication system transmits the WLAN information to the boundary area of the cell, in which the WLAN area 120 is not provided, so that transmission power is unnecessarily wasted.